1. Field of the Invention
The invention relates generally to devices and methods used to dispose tubewire into a radially surrounding tubing string.
2. Description of the Related Art
Coiled tubing has become a popular means for running a bottom hole assembly (“BHA”) or other tools into a subterranean wellbore. In most cases, it is desirable to be able to transmit electrical power down to the BHA or other tools as well as to permit control signals or sensed data to be transmitted between the surface and the downhole tools. Conventionally, this is done by disposing wireline into the coiled tubing. Wireline is a braided steel cable with layers of armor with conductors inside.
Use of wireline can be problematic. Wireline is prone to damage from acidic fluids in some instances. The slack in wireline must be adjusted over time, which requires time and money.
Tubewire is an alternative to wireline and has many advantages over wireline. Tubewire can be disposed inside coiled tubing to provide electrical power and a signal path from the surface to various downhole tools attached to the end of the coiled tubing. Tubewire is a tube that contains an insulated cable that is used to provide electrical power and/or data to the bottom hole assembly or to transmit data from the BHA to the surface. Tubewire is substantially inflexible relative to its wireline. Tubewire is available commercially from manufacturers such as Draka Cableteq of North Dighton, Mass.
Tubewire can be disposed into coiled tubing at the surface. Systems and methods for injecting and retrieving tubewire into and out of coiled tubing are discussed in U.S. Pat. No. 7,845,419 by Naumann, which is incorporated herein by reference in its entirety. While the coiled tubing is spooled up on a reel at surface, the tubewire is placed into the coiled tubing by pumping fluid through the coiled tubing at high flow rates while an injector is used to feed the tubewire into the coiled tubing by applying a pushing force. The inventors have determined that, occasionally, the tubewire can get stuck or stop moving during injection. As a result, the full motive force of the injector is applied to stationary tubewire, causing the tubewire to buckle and be permanently damaged. When tubewire buckles, it tends to take on a helical shape just prior to failure. The inventors have determined that coiled tubing has a large inside diameter (“ID”) relative to the outside diameter (“OD”) of the tubewire. Therefore, a relatively small axial force can cause the tubewire to buckle, plastically yield and fail inside the coiled tubing. The tubewire injector can easily generate the required axial force.
U.S. Pat. No. 7,845,419 by Naumann discussed the use of a flexible wand to mitigate buckling of tubewire during injection.